Geochemical Records Of Sediments In The Yangtze River Delta And Geochemical Province Of Mobile Muds In The Adjacent Waters

In recent decades,the sediment retention caused by the reservoirs in the Yangtze river basin,especially the Three Gorges Reservoir,have resulted in the significant riverbed erosion downstream the reservoir,and the sediment contributions from downstream tributaries were relatively increased.As a result,compositions and provenances of sediments in the middle and lower reaches have been changed.And the decrease of the sediment flux into the sea had been causing the change of the accretion/erosion in the estuary.Based on the above changes,it is necessary to reassess the influence on the compositions and provenances of sediments?mobile muds?in the Yangtze River delta and the adjacent waters.With the rapid economic development of the basin,the flux of the pollutant emission has been increasing obviously.Besides,the relative decrease of sediments caused the decline in the"self-cleaning"ability of water environment.Therefore,the response to above changes in the heavy metals contamination records and the influencing provinces of the heavy metals contamination in the study area need to be studied systematically.Based the parameters such as contents and ratios of elements in sediments?mobile muds?,the distribution patterns,anomalies and the results of continuous extraction method?BCR?,this study is aimed at studying the above-mentioned issues about provenances and heavy metals contamination of sediments?mobile mud?from the following aspects.Firstly,how the geochemical records in estuary sedimentss responded to the change of compositions and provenances of the sediments from the basin caused by human activities.Secondly,conduct the studies on the provenances based on the temporal and spatial distributive characteristics of mobile mud geochemical elements compositions in the South Yellow Sea and East China Sea.Thirdly,how the temporal and spatial distributive characteristics of heavy metals in sediments?mobile muds?responded to the increase of pollutant input in human activities.Following conclusions were drawn in the research:?1?The above changes occurred in the basin had caused significant influences on the depositional environment and the geochemical composition of core sedimentss in the Yangtze River Delta.The results of radioactive isotopic dating(²¹⁰Pb)indicated that the average deposition rate of the leading edge of the Yangtze River Delta had been decreased to the average value of 0.22cm/y.?2?Based on the relative contents of many metals elements?normalized by Al and Li?,the ratio of some metals elements?such as Ti/Mg and K/Ca?,the parameters of rare earth elements?such as the anomalies and fractionation?and the?La/Yb?_UCC-?Gd/Yb?_UCC correlation diagram,the study on the provenances of mobile muds in the East China Sea and the South Yellow Sea were conducted.The study found that materials from the Yangtze River were the major provenance of the area outside the Yangtze River estuary and the northern East China Sea inner continental shelf area.And the important provenance of sedimentss in the southern part of the inner continental shelf?south of 28�N?might include the material from the Taiwan rivers,while the Yangtze River played the major role as well.In addition,the main provenance in the South Yellow Sea was the material from Yellow River?Ancient Yellow River?,and another important provenance was from Yangtze River transported northward by the Changjiang River Diluted Water and East China Sea Shoal Coastal Current.The provenances of mobile mud in the middle continental shelf of the East China Sea were relatively complex.?3?Vertical distributive characteristics of the relative contents of heavy metals such as Cu,Cd,Pb?normalized by Li or Al?,the content and percentage of non-residual form of heavy metals showed that the accumulation of heavy metals in the sedimentss of the Yangtze River Delta appeared since 1970,and havd gradually deteriorated since1990.The spatial distributive characteristics of relative content of heavy metals,content and percentage of heavy metals non-residual form showed that there were heavy metals accumulation in different types,ranges and sources in mobile mud in the area outside out the Yangtze Estuary and the Zhejiang-Fujian Coastal Area only.Based on its distinguishing features such as continuous resuspension,the mobile muds have been successfully applied to the provenance tracing by elemental geochemistry and the assessment of heavy metals contamination in the Yangtze River Delta and its adjacent waters.In order to improve and enhance the scientific and practical value of mobile mud in the research of provenance trace,it is necessary to combine it with other scientific methods,...